Conical scanning antenna



March 9, 1954 J HALPERN r 2,671,854

CONICAL SCANNING ANTENNA Filed Sept. 6, 1945 MOTOR TO TRANSMITTER INVENTORS JULIUS HALPERN NORMAN F. RAMSEY ATTORNEY Patented Mar. 9, 1954 UNITED STATES PATENT OFFICE CONICAL SCANNING ANTENNA Application September 6, 1945, Serial No. 614,726

3. Claims. (01. 25033.65)

This invention relates in general to antenna systems, and more particularly to such systems embodying an eccentric rotating beam of elec-- tromagnetic energy.

In certain types of radio object-locating systems, a directional receiving antenna has a radiation pattern which is made to point in, a direction which is a few degrees different from the direction of the antenna axis. The antenna is rotated, which causes this eocentrically-pointing beam to rotate in synchronism with it. This scanning of space by a rotating eccentric beam is called conical scanning, because of the shape of the pattern of revolution made by the axis of the antenna beam.

All directional antenna patterns, however, have directions other than that of the main beam of smaller amounts of radiation. These side lobes in the radiation pattern, as they are called, are usually at an angle of a few degrees from the axis of the main beam, and are touching the main beam. These side lobes are undesirable in that they, as well as the main beam, will receive signals, and the apparent direction of the energy received by the antenna at any instant Will be somewhat ambiguous. A detailed explanation of conical scanning is given in application Serial No. 531,826, filed April 19, 1944, by Leland J. Haworth and Edward M. Purcell, entitled Communication System. Hereafter th term radiation pattern will mean the variation in sensitivity of the receiving antenna with an le from the antenna axis.

Among the obj cts of. th present invention, therefore, are:

To provide an antenna adaptable, to conic l scannin 2. To provide such an antenna whereby the abovementioned undesirable sheets of the side lobes of the antenna pattern are lessened.

In accordance with the present invention there is provided an antenna system in which the axis of the portion of the side lobes nearest the axis of revolution of the antenna at any time is made to be in substantially the same direction as the angle of the axis of the main lobe when it is diametrically opposite to its position at this time.

This invention will best be understood by reference to the drawings, in which:

Fig. 1 shows one type of antenna system which may be used in accordance with the present invention, and

Fig. 2 is a diagram of the present radiation pattern.

Referring now to a description of the apparatus and to Fig. 1, there is shown a functional diagram of one type of antenna system which could be used to obtain the radiation pattern of this invention. A circular wave guide 10 has energy fed into it from a radio-frequency trans mitter, noted but not shown. In front of the open end ll of the wave guide is a metallic re flector I2 and an insulating cup-shaped housing 13. Paraboloidal reflector I4 is mounted in such a manner that metallic reflector I2 is substantially at the focal point of the paraboloid. Motor I5 is mechanically coupled to wave guide 10, and causes the wave guide to rotate about its own axis, thus rotating components 12 and I3 also. In one embodiment, a reflector l4 also rotates in accordance with the turning of wave guide I 0. In another embodiment the reflector M is not physically connected to the guide Ill, and so does not rotate.

Referring now to the operation of the system, and to Fig. 1, electromagnetic energy is fed into wave guide In from the transmitter, not shown. Electromagnetic waves are sprayed out of the open end II of the wave guide In and are refiected back toward paraboloid M by metallic reflector I2. Insulating material 13 is such that it allows electromagnetic radiation to readily pass through it. The waves are then reflected from paraboloid M towards the right of the figure.

The type of antenna system described and illustrated herein has a highly directional'radiation pattern. If components IE) and 12 are mounted in a symmetrical manner with respect to the reflector I4, the axis of the directional beam will lie substantially along the axis of wave guide It. In the present system, however, the positioning of the components is asymmetrical, and the beam of the system will point in a direction that is a few degrees displaced from the direction of the axis of wave guide 10. Furthermore, as the guide It is rotated, this eccentrio beam will rotate also, its axis describing a cone-like surface in space.

Refer now to Fig. 2. The axis of wave guide It is represented by center line 20. In one position of rotation of guide In, the main beam of th radiation pattern will be in a position such as 2!, with its axis being represented by center line 22. The major sid lobes of beam 2| are lobes 23 and 24. A rotation of of Wave guide It will cause the main beam of the radiation pattern to be in a position 25, with its axis being represented by center line 26. The pattern for this position of the wave guide I0 is shown in dotted lines. The major sid lobes are shown as lobes 21 and 28.

In the present invention, the dimensions of paraboloidal reflector l4 and the amount of asymmetry of components It] and 12 are carefully chosen so that the side lobe 23 of the main lobe 2| closest to the axis of revolution 20 will have its axis lying along substantially the same line as the axis of the main lobe when it is in position 25, this being diametrically opposite to position 2| of the main lobe. Thus the angle between the major axis of the main lobe and the major axis of a side lobe will be equal to the apex angle of the conical surface described by the major axis of the main lobe. Or in other words, the cone described by the major axis of the main lobe is tangent to the cone described by the major axis of the side lobe.

That this procedure will reduce the ambiguity normally resulting from large side lobes can readily be seen. It must first be pointed out, however, that the purpose of a conical scanning radiation pattern is to compare the amplitude of the two signals received by two such lobes as 2| and 25 and so to determine the direction of the object causing the echo. It is seen that when the antenna is pointing towards the echo, the beams 2| and 25 each receive the same amount of energy. Let us assume that the side lobes are not positioned with respect to the main lobe in the manner mentioned above, and let the axis of one side lobe of beam 21 be represented by center line 29. Furthermore, let the radio echo be coming from a direction such as 29. At this angle, it is seen that the side lobe of beam 2| will receive as much energy as the main lobe 25. Thus while the antenna is rotating there will be no change in the amplitude of the received signal while the main beam is in position 2| over that while the main beam is in position 25, and it would be assumed that the radio echo is coming from the direction of axis 20, instead of its actual direction, that of axis 29.

' However, if the side lobe 23 of main lobe 2| is in the direction along the axis of beam 25, this ambiguity will be done away with. The main lobe 25 will give a very much stronger echo than side lobe 23, and there will be no question of the fact that the radio echo lies along the axis of revolution 20.

It is the angle of eccentricity of the axis of the paraboloidal reflector with respect to the axis of the guide H) which determine the angular swing of the main lobe. In practice, this angle is varied and the radiation pattern is taken at each angle. The angle used practically is the one which gives the radiation pattern according to Fig. 2.

This arrangement permits a relatively wide angle scan with the central cross-over point of the radiation pattern much nearer the source of radiation than in conical scanning systems heretofore used.

While there has been described what is at present considered the preferred embodiment of the invention it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, desired to claim all such changes and modifications as fall within the true spirit and scope of the invention.

We claim:

1. An antenna comprising a wave guide adapted to transfer electromagnetic energy, a paraboloidal reflector asymmetrically disposed about said wave guide, said wave guide passing through said reflector, a metallic reflector juxtaposed to one end of said wave guide and disposed substantially at the focal point of said paraboloidal reflector, and means for rotating said wave guide, whereby a beam of energy having a main lobe and at least one adjacent minor side lobe will be radiated, said wave guide and said paraboloidal reflector having an amount of asymmetry that upon rotation of said wave guide the angle between the major axis of said main lobe and the major axis of said side lobe adjacent thereto will be equal to the apex angle of the conical path described by the major axis of said main lobe.

2. The antenna of claim 1, further including an insulating cup-shaped housing mounted at the end of said wave guide facing said metallic reflector and serving to connect said metallic reflector to said wave guide, said metallic reflector being a disc.

3. An antenna comprising an electromagnetic energy transmission element, a reflector asymmetrically disposed about said element, said reflector and element radiating electromagnetic energy in the form of a beam having a main lobe and at least one adjacent minor side lobe, and means coupled to said antenna for rotating said beam so that the major axes of said main lobe and said minor side lobe of said beam describe a pair of conical surfaces, the said element and reflector having an amount of asymmetry that said conical surfaces are tangent to one another.

JULIUS HALPERN. NORMAN F. RAMSEY.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,934,078 Ludenia Nov. 7, 1933 2,206,923 Southworth July 9, 1940 2,342,721 Boemer Feb. 29, 1944 2,370,053 Lindenblad Feb. 20, 1945 2,409,183 Beck Oct. 15, 1946 2,419,556 Feldman Apr. 29, 1947 2,531,454 Marshall Nov. 28, 1950 2,531,455 Barrow et al. Nov. 28, 1950 FOREIGN PATENTS Number Country Date 450,484 Great Britain July 20, 1936 

